1. Expression and Function of Asialo GMI (AsGMI) in Alloreactive Cytotoxic T Cells (CTL) and in Lymphokine-Activated killer LAK cells. AsGMI was expressed differently in CTL and LAK cells. AsGMI was expressed on the LAK precursors but its expression disappeared when LAK precursors were fully differentiated into effectors. The reverse was true for CTL, AsGMI was not expressed on CTL precursors but was readily demonstrable in 3- day-cultured CTL. Among eleven CTL clones tested, AsGMI was found to be expressed on a majority (7 our of 8) of L3T4- CTL clones. The cytotoxicity mediated by AsGMI+ cloned CTL was blocked by alpha AsGMI or AsGMI alone, indicating that AsGMI is involved in the CTL- target interaction to mediate lytic reaction. 2. Tumor Immunology. Activated killer (AK) cells were generated in spleen cell culture derived from tumor bearing hosts (TS). In many aspects, these AK cells resembled LAK cells. The major difference was that the LAK precursors from normal hosts were AsGMI+ cells and the LAK precursors from TS were AsGMI-, suggesting that the latter was in an "activated" state. These findings indicate that in the tumor bearing hosts, tumor cells trigger the activation of LAK precursors, but the same tumor cells may be immunosuppressive which prevents the full differentiation of LAK precursors into LAK effectors.